1. Field of the Invention
The present invention relates generally to an ink-jet printing method and an apparatus therefor in which suction recovery operation is performed for maintaining reliability of an ejecting function of a printing head performing printing by ejecting an ink droplet.
2. Description of the Related Art
A printing apparatus, such as for a printer, a copy machine, facsimile and so forth, is generally constructed to print an image consisted of a dot pattern on a printing medium, such as a paper, plastic film, cloth or so forth on the basis of an image information.
Such printing apparatus can be classified as an ink-jet type, a wire-dot type, laser-beam type and so forth based on its printing system.
A printing apparatus employing the ink-jet system performs printing by ejecting an ink on a printing medium. Such a printing apparatus holds advantages in capability of high speed printing of high definition image, lesser noise for non-impact type printing, and easiness of printing of a color image using multi-color inks.
Furthermore, a bubble-jet printing system proposed by the owner of the present invention can more easily realize high resolution and high speed printing. In such printing system, it is an important technology to maintain reliability of an ink ejecting function of a printing head in order to avoid influence of evaporation of ink, admixing of fine bubble or so forth for printing quality.
As typical technology for maintaining reliability of the ink ejecting function, a preparatory ejection process and a suction recovery process can be considered.
The preparatory ejection process is to perform ejection of ink at a position out of the printing medium. By this process, the ink degraded in viewpoint of ejection performance and printing quality due to partial evaporation of a volatile component is ejected through ejection openings which have not been used a while, for maintaining good printing quality.
Such preparatory ejection is a measure for evaporation of ink and has to be performed frequently at high environmental temperature or when elevation of temperature in the printing head is large. It should be noted that an interval of the preparatory ejection process is variable depending upon a construction of the printing head and/or physical property of the ink. However, the interval is typically several seconds to several tens of seconds. For performing the preparatory ejection, the time interval to next preparatory ejection is set on the basis of an instantaneous environmental temperature and degree of temperature elevation of the printing head.
On the other hand, the suction recovery process is a process to position the printing head in opposition of a cap for capping, and thereafter to suck the ink in the printing head via the cap by means of a suction pump for appropriately filling the printing head with the ink when bubble is present in an ink passage storing the ink to be ejected, when recovery by preparatory operation becomes insufficient due to evaporation of the ink in the ink passage or when the ink is consumed out from the ejection opening, the ink passage and an ink chamber.
It should be noted that, in the conventional a bubble-jet printing apparatus, growth speed of bubble depending upon difference between the environmental temperature of the printing head (for example, ink temperature within the ink tank) and the temperature in the ink passage and the ink chamber, is not taken into account in the technology for maintaining reliability. Thus, it can be caused unnecessarily frequent sucking operation to result in lowering of throughput and increasing of waste ink. Conversely, it is also possible to have excessively long interval between suction recovery to result in printing failure.